Such a sensor is used, for example, to detect a pressure of a swimmer on a plate of a timing system for swimming competitions referred to as a touch plate. A plate of this type is secured to the finishing wall of the swimming pool and a pressure of a swimmer on the touch plate causes the plate to come closer to the wall. When this approach movement is detected by the sensor, the chronometer measuring the swimmer's time stops or records an intermediate time.
Inductive displacement sensors usually comprise a coil excited by a high-frequency alternating current supplied by a detector circuit. The proximity of an electrically conductive or ferromagnetic part with the coil causes a loss within the magnetic circuit formed by the coil, the part and air gap separating them, or/and modifies the inductance of the coil. The measurement of loss in the circuit or of a variation in this inductance thus allows a displacement of the part in relation to the coil to be identified.
The disadvantage of this type of detector circuit is that current is being permanently consumed there. There is therefore a need for a detector circuit of lower consumption, which allows indication that a loss threshold in the magnetic circuit or its inductance has been exceeded (threshold value corresponding, for example, to a pressure of a swimmer on a touch plate).